1. Field of the Invention
This invention relates to a hollow-fiber membrane module for treating a liquid using hollow-fiber membranes. More particularly, this invention relates to a hollow-fiber membrane module used for dialysis of blood or used for purification of water such as sewage or wastewater.
2. Description of Related Art
As is well known, for example for dialysis of blood, a hollow-fiber membrane module composed of hollow-fiber membranes (semipermeable membranes) is used. Such a hollow-fiber membrane module comprises a cylindrical casing having an inlet port for the treating liquid at one end and an outlet port for the treating liquid at the other end, a hollow-fiber membrane bundle contained in the cylindrical casing, and potting layers for fixing the hollow-fiber membrane bundle to the inner wall of the cylindrical casing at both the ends of the hollow-fiber membrane bundle, to ensure that a dialyzing fluid can be made to flow in the cylindrical casing from the inlet port toward the outlet port, while blood can be made to flow in the hollow-fiber membranes from the outlet port side toward the inlet port side, for dialysis of blood (see JP7-37700Y).
The above-mentioned hollow-fiber membrane module is obtained by inserting a hollow-fiber membrane bundle slightly longer than a cylindrical casing, into the cylindrical casing made of a plastic material such as polypropylene, polyethylene, polyethylene tetrafluoride, polyester, polycarbonate, or ABS (acrylonitrile-butadiene-styrene), potting the inserted hollow-fiber membrane bundle at its both ends with a polymeric material such as polyurethane or silicone for fixing it at both the ends, cutting off the potting ends using a sharp knife, to open the hollow-fiber membranes at the potting end faces, and installing headers to surround the openings of the cylindrical casing entirely. In this hollow-fiber membrane module, the potting portions function as potting layers. When a potting end is cut off, a force for separating the potting end from the cylindrical casing acts, and in the case where the cylindrical casing is made of a slightly adhesive plastic material such as polypropylene, polyethylene or polyethylene tetrafluoride, it can happen that the potting layer peels or comes off from the cylindrical casing.
It is also proposed to install cylindrical hollow-fiber membrane bundle holders separate from the cylindrical casing at both the ends of the hollow-fiber membrane bundle, in such a manner that the hollow-fiber membrane bundle holders can be bonded to the inner wall of the cylindrical casing. However, since the holders merely support the hollow-fiber membrane bundle without disturbing them, they do not work sufficiently for preventing the potting layers from peeling or coming off. If a potting layer should peel from the cylindrical casing, even though it does not come off, for example in the event of dialyzing blood, the dialyzing fluid and blood are mixed, and normal dialysis cannot be made. Such a membrane module must be thrown away. Furthermore, since it is necessary to manufacture the hollow-fiber membrane bundle holders separately from the cylindrical casing and to install them in the casing beforehand, the increase in the number of parts and the increase in the assembling man-hours raise the production cost of the hollow-fiber membrane module.